According to present practice, terephthalic acid is manufactured from p-xylene by oxidation, in particular. Other forms of xylene (meta and ortho) can be converted to be suitable, for example, by the Henkel reaction or its modification. The Henkel reaction is an industrial-scale process, wherein the alkali salts of aromatic acids are re-arranged using a thermal reaction in the presence of a metallic salt, such as cadmium salt (see, for example, DE 936036).
Terephthalic acid is mainly used as the precursor of polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). PET is used, among others, for the manufacture of fibers for the clothing industry, the manufacture of plastic containers, such as plastic bottles, and for polymeric coating of paper or board in the packaging industry. In the manufacture of PET, generally, a catalyzed process is used, where an aromatic acid and an aliphatic diol are made to react together in the catalyzed process, wherein the catalyst contains, for example, titanium (among others, EP 2 003 159) or antimony (among others, GB 2 398 073).
Bio-based raw materials that are suitable for the manufacture of PET, for example, can be found on the market to an increasing extent, but a central problem when manufacturing this bio-based PET, however, is to find a uniform bio mass-based raw material suitable for the purpose; for example, for the manufacture of terephthalic acid, which is used in the manufacture of PET, by an industrial-scale process. The aliphatic portion of such corresponding polyesters, that is, the diol mentioned above, is already available from bio-based sources, but it is more difficult to find the source of a suitable aromatic part.
The conventional raw material for the manufacture of aromatic monomers has comprised crude oil. The aromatic fractions obtained from the fractional distillation of crude oil have been further processed to obtain aromatic monomers, unsubstituted or substituted, such as benzene, xylene and phenol. In addition to the aromatic fractions, aliphatic fractions are recovered from the source material and used as the raw material of polymers, among others.
As a substitutive alternative for fossil raw materials, sources of renewable organic raw materials have been explored for the manufacture of polymers. An ideal source of raw material for the aromatic monomers suitable for the manufacture of terephthalic acid would comprise wood that has abundant reserves; the by-products of the manufacturing process of chemical pulp, such as tall oil, in particular.
The specification of US-2004/0230085 discloses the catalytic hydrodeoxygenation of tall oil fatty acids as part of the manufacture of a diesel fuel of biological origin. The deoxygenation is carried out by gaseous hydrogen in a catalyst bed, where there is a metallic catalyst, such as NiMo or CoMo, and the carrier comprises alumina and/or silica. From the gas mixture created at the deoxygenation stage, oxides of carbon and various impurities are separated, and the purified hydrogen is circulated back to the process. At the second stage of the process, isomerization is carried out for the liquid phase, converting the product into a form suitable for use as fuel. Since the isomerization stage is sensitive to aromatic and naphthene impurities, tall oil resin acids, from which they can be formed in the deoxygenation, are removed from the source material as effectively as possible. In the example 1 of the specification, there were 1.9% of resin acids among the fatty acids.
The specification of US-2008/0154073 discloses a similar process for the manufacture of diesel fuel from biorenewable raw materials, such as vegetable oils. As a potential raw material, tall oil is mentioned, comprising resin acids in addition to fatty acids, but according to test results, tall oil produced a considerable portion of hydrocarbon fractions heavier than diesel, unlike the soybean oil that was also used in the tests.
The specification of US-2007/0135669 also describes the manufacture of diesel fuel from biorenewable raw materials and observes the unwanted presence of unsaturated and aromatic hydrocarbons in the end product. The specification discloses the invention of a process, wherein the fatty acids distilled from tall oil are first isomerized and thereafter, at the second stage of the process, deoxygenated.
The specification of WO-2009/004181 A2 discloses the catalytic hydrocracking of vegetable oils and the subsequent steam cracking into monomers suitable for polymerization. The vegetable oils mentioned in the specification do not contain resin acids of tall oil.
The specification of U.S. Pat. No. 5,705,722 A discloses the catalytic hydrocracking of a mixture of tall oil fatty and resin acids and the use of the obtained product as additives of diesel fuel. The publication, however, does not disclose the recovery of aromates.